The invention concerns a pharmaceutical agent being active against multidrug resistant cell lines and comprising epothilone A-N-oxide of the following formula: and/or epothilone B-N-oxide of the following formula: as active ingredient facultatively in the presence of usual auxiliary agents, carriers and/or diluents.

As regards epothilone A and epothilone B reference is made to DE-A-41 38 042.

Epothilone A N-oxide: 100 mg of 70% m-chloroperbenzoic acid in 0.5 ml of dichloromethane were added to 100 mg of epothilone A in 1 ml of dichloromethane. After the mixture has been stirred for 6 hours at room temperature, it is diluted with dichloromethane and extracted by shaking in succession with sodium sulphite solution to destroy excess peracid and with sodium bicarbonate solution. The solvent is evaporated in vacuo, and the residue is separated by preparative HPLC on a Nucleosil RP-18 column (250 × 20 mm, eluent methanol/water 60:40). Yield 60 mg of colourless oil.

• R_f=0.60 (silica gel TLC aluminium foil, eluent dichloromethane/methanol 9:1);
• ESI-MS (neg. ions) m/z 510;
• UV (methanol): lamda max. 240 nm;
• ¹³C NMR (CDCl₃): C-1 170.5, C-2 39.9, C-3 70.8, C-4 55.1, C-5 221.4, C-6 40.9, C-7 72.9, C-8 37.6, C-9 31.8, C-10 22.8, C-11 28.0, C-12 58.0, C-13 55.8, C-14 32.2, C-15 75.5, C-16 144.5, C-17 111.4, C-18 143.4, C-19 110.3, C-20 145.6, C-21 13.5, C-22 15.4, C-23 23.3, C-24 12.0, C-25 16.5, C-27 18.2 ppm;
• ¹H NMR (CDCl₃): 2a-H 2.12 dd, 2b-H 2.47 dd, 3-H 4.55 dd, 3-OH 6.48 broad, 6-H 3.25 dq, 7-H 3.72 dd, 8-H 1.81 m, 9a-H 1.34 m, 9b-H 1.56 m, 10-H₂ 1.48 m, 11a-H 1.27 m, 11b-H 1.87 m, 12-H 2.92 ddd, 13-H 2.98 m, 14a-H 1.67 ddd, 14b-H 2.23 d, 15-H 5.33 d, 17-H 6.82 s, 19-H 7.09 s, 21-H₃ 2.61 s, 22-H₃ 1.02 s, 23-H₃ 1.42 s, 24-H₃ 1.18 d, 25-H₃ 0.99 d, 27-H₃ 2.04 s ppm.

To a solution of 2 mmol of m-chloroperbenzoic acid in 1 1 ml dichloromethane were added 507 mg (1 mmol) of epothilone B and stirred for 3 h at room temperature. Ethyl acetate was added and excess of perbenzoic acid was reduced with an aquous solution of sodium sulfite. The organic layer was dried with magnesium sulfate and evaporated to give 0.6 g of crude product containing 390 mg (75%) of the desired product according to HPLC analysis. Separation was achieved by chromatography on a HD-SIL C-18, 35-70 µm column (9 cm φ, length 83 cm) with the solvent system 45% acetonitrile/55 % ammonium acetate buffer 50 mM, pH 7.5; detection 254 nm. Yield 207 mg.

• DC:R_f=0.19 (silica-gel Si60, dichloromethane/methanol 95:5, detection with vanillin/-sulfuric acid, blue-gray coloration on heating to 120°C);
• HPLC:R_t = 4.1 min (Nucleosil, C-18, 7 µm, 250 x 4 mm column, solvent system methanol/water 70:30, 1 ml/min, detection at 254 nm);
• UV (MeOH): λ_max (ε) = 283 sh (log ε 3.22), 264 sh (3.63) 236 nm(4.19);
• IR (KBr): $\overline{\text{ν}}$ = 3439, 2963, 2936, 2877, 1740, 1689 cm^-1;
• ¹H-NMR (CDCl₃) : δ = 2.13 (dd, J = 12.9, 12.0, 2-Ha); 2.47 (t=12.0, 2-Hb); 4.58 (m, 3-H); 3.29 (dq, J = 2.0, 5.8, 6-H); 3.70 (d, J = 5.8, 7-H); 1.20 - 1.90 (m, 8-H, 9-H₂, 10-H₂, 11-H₂); 2.75 (m, 13-H); 1.66 (m, 14-Ha); 2.23 (dbr, J = 15.6, 14-Hb); 5.32 (d, J = 11.6. 15-H); 6.79 (sbr, 17-H); 7.08 (s, 19-H); 2.60 (s, 21-H₃); 1.02 (s, 22-H₃); 1.27 (s, 23-H₃); 1.16 (d, J = 6.8, 24-H₃); 0.99 (d, J = 7.1, 25-H₃); 1.41 (s, 26-H₃); 2.07 (s, 27-H₃);
• ¹³C-NMR (150 MHz, CDCl₃): δ = 170.5 (C-1), 40.0 (C-2), 70.9 (C-3), 55.1 (C-4), 221.4 (C-5), 40.7 (C-6), 72.5 (C-7), 37.3 (C-8), 31.5 (C-9), a 22.0 (C-10), 33.3 (C-11), b 62.3 (C-12), 63.0 (C-13), 33.4 (C-14), 75.6 (C-15), 144.3 (C-16), 111.1 (C-17), 143.3 (C-18), 110.3 (C-19), 144.7 (C-20), 13.4 (C-21), 15.3 (C-22), 23.2 (C-23), 12.5 (C-24), 16.5 (C-25), 22.2 (C-26), 18.2 (C-27);
• [a] EI-MS (70 eV) : m/z (%) 523.2604 (40 M⁺), ber. (C₂₇H₄₁NO₇S) 523.2629, 424 (38), 336 (42), 194(18) 182(75), 154(100), 126(42).